Buildings typically use HVAC systems to selectively control indoor temperature, pressure, ventilation rate and other variables. One particular application of HVAC systems is for the cooling and humidity control of data centers. HVAC systems for this application typically include one or more HVAC units that are floor standing, but may also be wall-mounted, rack-mounted or ceiling-mounted. The HVAC units provide cooled air either to a raised-floor plenum, to a network of air ducts, or to the open air of the data center. Importantly, maintaining data centers at desired temperatures helps prevent computer hardware within the data center from overheating and malfunctioning.
In connection with the above, one of the key issues facing the data center industry in particular is the potential for loss of external electrical power. Loss of external power can have enormous negative effects on the data center, the IT hardware in the center, and the actual data that is being processed when such an event occurs. Most modern data centers employ some form of uninterruptable power supply (“UPS”) that is configured to automatically switch to a battery backup system when the supply of main electrical power is interrupted in order to keep the IT servers running for a limited period of time. During such limited period of time, the backup generator systems serving the data center can be started and/or the data center staff can initiate a shutdown cycle for the serves to prevent the loss of data. However, because roughly half of the electrical demand in a data center is produced by the HVAC equipment that cools the IT equipment, many data centers lack UPS back up for their HVAC systems and instead rely solely upon a rapid recovery via the generator sets.
Several things can occur in rapid succession in this conventional arrangement. First, if the IT equipment is operating at the new elevated inlet temperatures recommended by ASHRAE, the equipment is already operating closer to automatic shutdown temperatures. When the HVAC system fails as a result of an electrical power interruption, the server temperatures rise rapidly past their safe operating threshold and they shut themselves down in mid-process. This rapid rise in temperature can occur in seconds once a loss in power occurs. The second event is the startup cycle for the generators, which can take anywhere from 1 to 5 minutes. As will be readily appreciated, however, this is too long given the rapid IT equipment temperature rise. Finally, if the data center uses a chiller system the chillers themselves can take up to 10 minutes to restore full capacity.
In view of the above, there is a need for an improved means for maintaining operation of an HVAC system in the event of a loss of electrical power, without the need for connection to an external backup generator or other alternative power source.